CHAPTER SEVENTH.
Geometrical Details.—Calculation of the Capacity of the Balloon.—The Double Receptacle.—The Covering.—The Car.—The Mysterious Apparatus.—The Provisions and Stores.—The Final Summing up.
Dr. Ferguson had long been engaged upon the details of his expedition. It is easy to comprehend that the balloon—that marvellous vehicle which was to convey him through the air—was the constant object of his solicitude.
At the outset, in order not to give the balloon too ponderous dimensions, he had decided to fill it with hydrogen gas, which is fourteen and a half times lighter than common air. The production of this gas is easy, and it has given the greatest satisfaction hitherto in aerostatic experiments.
The doctor, according to very accurate calculations, found that, including the
